In recent years, a group III-V nitride semiconductor expressed by a general formula AlxGa1-x-yInyN (0≦x≦1, 0≦y≦1, x+y≦1) has been widely used as a semiconductor material for a light emitting device which operates within a wavelength band ranging from the visible wavelength to the ultraviolet wavelength and for an electronic device which operates at high power and at high temperature.
When a semiconductor light emitting device made of the group III-V nitride semiconductor is formed on a sapphire substrate, an intermediate layer made of GaInN is generally formed between the substrate and an active layer in order to suppress propagation of a crystal defect to the active layer, the crystal defect being caused by a lattice mismatch between the substrate and a group III-V nitride semiconductor layer (for example, see Patent Document 1).
Meanwhile, as a substrate used for a light emitting device made of a group III nitride semiconductor, a conductive substrate such as a GaN substrate has been used as an alternative to an insulating substrate such as a sapphire substrate.
When the conductive substrate is used, a current can be conducted through the substrate to lower the resistance value of a current path, which allows electric power consumption and the operating voltage to be reduced. Moreover, the electrostatic withstand voltage can be enhanced.
FIG. 6 shows an example of a conventional semiconductor light emitting device using the GaN substrate. In FIG. 6, on a GaN substrate 111, an n-type GaN layer 102, a GaInN active layer 106, and a p-type GaN layer 112 are sequentially stacked.
On the p-type GaN layer 112, a p-side electrode 109 is formed. Parts of the p-type GaN layer 112, the GaInN active layer 106, and the n-type GaN layer 102 are removed to expose part of the n-type GaN layer 102. On the exposed part of the n-type GaN layer 102, an n-side electrode 110 is formed (for example, see Patent Document 2).
The lattice mismatch ratio is smaller between a GaN substrate and a group III nitride semiconductor layer formed on the GaN substrate than between a sapphire substrate and a group III nitride semiconductor layer formed on the sapphire substrate. Therefore, the group III nitride semiconductor layer formed on the GaN substrate has few defects caused by the lattice mismatch, and thus there is no need to suppress the propagation of the crystal defect caused by the lattice mismatch with the substrate. Moreover, since an intermediate layer made of GaInN grown at low temperature may also be a cause of a crystal defect which is naturally produced during the growth, the intermediate layer made of GaInN which is lattice-mismatched with the GaN substrate is not formed.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 8-70139
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2001-60719